As is known, the majority of four-wheel drive vehicles are equipped with a transfer case mounted to a multi-speed transmission for directing power from the engine to all four wheels. To accommodate different road surfaces and conditions, many transfer cases are equipped with a mode shift mechanism which permits the vehicle operator to selectively couple the non-driven wheels to the driven wheels for establishing a part-time four wheel drive mode in addition to the two-wheel drive mode. As an alternative, some transfer cases are equipped with a transfer clutch that is passively or actively controlled in response to driveline slip for automatically delivering drive torque to the non-driven wheels for establishing an on-demand four-wheel drive mode. In addition, some transfer cases are also equipped with a two-speed range shift mechanism for permitting the vehicle operator to select between high-range and low-range four-wheel drive modes.
Automobile manufacturers continuously strive to reduce vehicle weight and improve vehicle noise, vibration and harshness (NVH) characteristics. In particular, sport utility vehicles (SUV) enjoy a significant portion of the overall vehicle market. The majority of these SUV's provide a four-wheel drive mode and, therefore, are typically equipped with a transfer case. As part of the vehicle's driveline, a transfer case has significant influence on the NVH characteristics of the vehicle. For example, vibrations and excitations generated by the transmission are transferred through the transfer case to front and rear propshafts. Additionally, the transfer case itself can be a source of NVH excitation.
One critical characteristic of four-wheel drive vehicles is the weight of the transfer case. Specifically, the shafts used in transfer cases are generally manufactured from solid forgings which are machined to form various gear segments, bearing and stop surfaces, as well as other features along the length of the shaft. Furthermore, traditional transfer cases include a multi-piece cast housing which includes at least two housing sections that are bolted together for enclosing and supporting the internal components. Because the housing sections are bolted together, each section requires a peripheral flange through which the bolts extend. In view of the recognized needs to reduce vehicle weight for improved fuel economy and to improve vehicle NVH characteristics, it is desirable to develop a light-weight transfer case providing improved NVH characteristics.